Sedentary Work Exerting up to 10 pounds (4.5 kg) of force occasionally and/or a negligible amount of force frequently or constantly to lift, carry, push, pull, or otherwise move objects, including the human body. Sedentary work involves sitting most of the time, but may involve walking or standing for brief periods of time. Jobs are sedentary if walking and standing are required only occasionally and other sedentary criteria are met.

Light Work Exerting up to 20 pounds (9.1 kg) of force occasionally and/or up to 10 pounds (4.5 kg) of force frequently, and/or negligible amount of force constantly to move objects. Physical demand requirements are in excess of those for Sedentary Work. Light Work usually requires walking or standing to a significant degree. However, if the use of the arm and/or leg controls requires exertion of forces greater than that for Sedentary Work and the worker sits most the time, the job is rated Light Work.

Medium Work Exerting up to 50 (22.7 kg) pounds of force occasionally, and/or up to 25 pounds (11.3 kg) of force frequently, and/or up to 10 pounds (4.5 kg) of forces constantly to move objects.

Heavy Work Exerting up to 100 pounds (45.4 kg) of force occasionally, and/or up to 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Very Heavy Work Exerting in excess of 100 pounds (45.4 kg) of force occasionally, and/or in excess of 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Job Classification

In most duration tables, five job classifications are displayed. These job classifications are based on the amount of physical effort required to perform the work. The classifications correspond to the Strength Factor classifications described in the United States Department of Labor's Dictionary of Occupational Titles. The following definitions are quoted directly from that publication.

Sedentary Work Exerting up to 10 pounds (4.5 kg) of force occasionally and/or a negligible amount of force frequently or constantly to lift, carry, push, pull, or otherwise move objects, including the human body. Sedentary work involves sitting most of the time, but may involve walking or standing for brief periods of time. Jobs are sedentary if walking and standing are required only occasionally and other sedentary criteria are met.

Light Work Exerting up to 20 pounds (9.1 kg) of force occasionally and/or up to 10 pounds (4.5 kg) of force frequently, and/or negligible amount of force constantly to move objects. Physical demand requirements are in excess of those for Sedentary Work. Light Work usually requires walking or standing to a significant degree. However, if the use of the arm and/or leg controls requires exertion of forces greater than that for Sedentary Work and the worker sits most the time, the job is rated Light Work.

Medium Work Exerting up to 50 (22.7 kg) pounds of force occasionally, and/or up to 25 pounds (11.3 kg) of force frequently, and/or up to 10 pounds (4.5 kg) of forces constantly to move objects.

Heavy Work Exerting up to 100 pounds (45.4 kg) of force occasionally, and/or up to 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Very Heavy Work Exerting in excess of 100 pounds (45.4 kg) of force occasionally, and/or in excess of 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Specialists

Comorbid Conditions

Factors Influencing Duration

The factors most likely to influence disability are the severity of the attack, the development of complications, whether episodes are acute or part of a chronic condition, any underlying chronic medical conditions, the individual's type of work, and most importantly, the individual's compliance with prescribed treatment.

Overall, the chronic, well-managed, mild to moderately severe asthmatic may experience very few days lost from work due to the disease. Smokers and individuals regularly exposed to known allergens are at greater risk for severe asthma with complications and increased duration.

Medical Codes

ICD-9-CM:

493.00 -

Asthma, Extrinsic, without Mention of Status Asthmaticus

493.01 -

Asthma, Extrinsic, with Status Asthmaticus

493.02 -

Asthma, Extrinsic, with (Acute) Exacerbation

493.10 -

Asthma, Intrinsic, Unspecified

493.11 -

Asthma, Intrinsic, with Status Asthmaticus

493.12 -

Asthma, Intrinsic, with (Acute) Exacerbation

493.20 -

Asthma, Chronic Obstructive, Unspecified

493.21 -

Asthma, Chronic Obstructive, with Status Asthmaticus

493.22 -

Asthma, Chronic Obstructive, with (Acute) Exacerbation

493.81 -

Exercise Induced Bronchospasm

493.82 -

Cough Variant Asthma

493.90 -

Asthma, Unspecified, Unspecified

493.91 -

Asthma, Unspecified, with Status Asthmaticus

493.92 -

Asthma, Unspecified, with (Acute) Exacerbation

Overview

Asthma is a chronic inflammatory obstructive disease of the airways in which, depending on severity, airflow out and in the lungs may be blocked by bronchial muscle constriction (bronchospasm), swelling of airway tissue, and excess mucus. Asthma is characterized by acute episodes of obstructed breathing that occur with the narrowing of breathing passages, making it difficult to inhale but even more difficult to exhale. With mild asthma, the airways are relatively normal between attacks. In more severe asthma, there is some degree of constant airway constriction, with additional narrowing that occurs during an acute attack. Typical symptoms include wheezing, shortness of breath (dyspnea), chest tightness, and coughing.

Many types of cells, including mast cells, eosinophils, T and B lymphocytes, macrophages, and neutrophils, as well as humoral elements (IgE antibodies), are responsible for the stimulation of smooth muscle and the chronic inflammatory changes in the airway that are characteristic of asthma. Production of these cells and humoral elements by the immune system of individuals with asthma is an exaggerated response (type I hypersensitivity reaction) triggered by various stimuli in the environment that are innocuous for individuals who do not have asthma. Individuals with asthma may have recurrent episodes of inflamed, narrowed airways when exposed to certain environmental triggers. Asthma attacks can be associated with varying degrees of airflow obstruction. Acute or chronic inflammation may also result in increasing bronchial responsiveness to triggers. The degree of hyper-responsiveness usually correlates directly with the severity of asthma.

Asthma symptoms can be triggered by allergens or irritants, upper respiratory tract infections (URI), stomach acid flowing back up the esophagus (gastroesophageal reflux disease [GERD]), certain medications or foods, anxiety, and exercise (exercise-induced asthma [EIA] or exercise-induced bronchospasm [EIB]). Individuals with allergic rhinitis (hay fever) are more likely to develop allergic asthma. Symptoms of asthma and allergic rhinitis can be triggered by seasonal or year-round allergens, which can include airborne pollens and molds, animal dander (dead skin flakes), house dust mite and cockroach droppings, and indoor molds.

Work related asthma consists of two entities. Occupational asthma is generally defined as a respiratory disorder directly related to inhalation of fumes, gases, dust, enzymes, metals, animal proteins, fungi, pollens, pharmaceutical agents, or other potentially harmful substances while on the job. With occupational asthma, symptoms of asthma may develop for the first time in a previously healthy worker, or pre-existing asthma may be aggravated by exposure within the workplace (work-exacerbated asthma). Occupational asthma has become the most prevalent work-related lung disease in developed countries.

Incidence and Prevalence: In 2011, a Centers for Disease Control and Prevention (CDC) survey found that approximately 20.5 million (8.8 percent) of adults residing in the United States and 8.6 percent of children from thirty-four states and Washington, D.C. reported currently having asthma (American Lung Association). Asthma remains the number one cause of admission to the hospital for children (Schraufnagel). In the U.S. in 2009, asthma caused 3,388 deaths, 479,300 hospitalizations, 1.9 million emergency room visits, and 8.9 million doctor visits (CDC). Nearly 3 out of every 5 asthmatics limit their usual activity because of their asthma (CDC).

Asthma is most prevalent in the Americas, Europe, and Australia. A western pattern of living which results in fewer severe infections early in life (hygiene hypothesis), greater use of antibiotics, consumption of more processed foods, and a shift from rural to urban living, is associated with an increased prevalence of asthma. Finally, in countries with a less Western lifestyle, the prevalence of asthma is low and remains so until westernization takes hold (Schraufnagel).

Causation and Known Risk Factors

Susceptibility to allergic asthma appears to be an inherited trait. Genetic factors significantly influence predisposition for developing any type of asthma, but environmental factors are necessary for the onset of the disease (Schraufnagel). Children are more likely to have asthma than adults. Among adults, those aged 18 to 24 are more likely to have asthma than older adults. More boys have asthma than girls (male to female ratio 2:1) until puberty, when the prevalence becomes equal; in adulthood, more women have asthma than men. Asthma occurs in all races. Blacks have more asthma attacks and are 2 to 3 times more likely than any other race to be hospitalized for asthma attacks and to die from asthma.

Diagnosis

History: A complete medical history is obtained, including the presence of typical symptoms (recurrent episodes of wheezing, shortness of breath, cough, chest tightness, sputum production, decreased exercise tolerance); any patterns associated with symptoms (time of day, season); duration, severity, and frequency of symptoms; age at onset and course of disease (emergency room visits, hospitalizations, ICU admissions, intubations); known precipitating or aggravating factors; other medical conditions; current medications; family history (asthma, allergy, rhinitis, eczema); social history (exposure to smoke); occupational history; and recreational history.

Intervals between attacks can be days, months, or years; for some people asthma can be a daily problem. The symptoms of asthma vary and are related to the severity of airway obstruction. Individuals may only be able to speak in one- to two-word sentences. If severe airway obstruction interferes with the delivery of oxygen to the brain, individuals can become restless and confused. Exercise may precipitate asthma. Between attacks, symptoms are absent or greatly reduced. Any information about events preceding an attack can be useful to determine a possible trigger for the asthma, but in some cases of hyper-reactive airways, it can be difficult to isolate the cause(s).

Symptoms of occupational asthma are the same as nonoccupational asthma and may include wheezing, dyspnea, chest tightness, and cough. Other associated symptoms may include runny nose, nasal congestion, and eye irritation. The cause may be allergic or nonallergic in nature, and the disease may persist for a lengthy period in some workers, even after they have discontinued exposure to the irritants that triggered their symptoms. Commonly, symptoms worsen through the workweek, improve over the weekend or while on vacation, and recur when the worker returns to the job.

Physical exam: Physical examination begins with observation of the patient. Signs of respiratory distress may include increased rapid breathing (tachypnea), a rapid heart rate (tachycardia), using the accessory muscles to help breathe, sweating (diaphoresis), and a bluish tinge to the skin (cyanosis). Use of a stethoscope to listen to the chest (auscultation) may reveal wheezing that is more prominent on exhalation and decreased breath sounds. The examination of an individual with asthma may be completely normal between attacks.

The nose may be examined for the presence of nasal polyps, any other type of nasal obstruction, and signs of allergic rhinitis. The skin may be examined for signs of atopic dermatitis, eczema, or other allergic skin conditions.

Tests: Pulmonary function testing (spirometry) is important in establishing the diagnosis of asthma and should be performed before treatment and after administration of a short-acting bronchodilator. During an acute asthmatic attack, spirometry will show diminished lung capacity and flow rate (peak flow) on exhalation. The diagnosis of asthma cannot be made solely on the basis of spirometry, since many other diseases cause similar findings. Also, pulmonary function may appear normal between asthma attacks. Arterial blood gases and an electrocardiogram (ECG) may be indicated if the asthma attack is severe and/or prolonged.

Peak flow testing is a simple and highly effective tool that can be used at home to monitor response to medications and detect exacerbations early, although it is not a substitute for spirometry. Peak flow should be monitored on arising before use of a bronchodilator.

Methacholine challenge tests can be used in special circumstances to diagnose hyper-reactive airways when pulmonary function tests are normal and asthma is suspected. If asthma is present only on the job, it may be necessary to measure airflow in the workplace with a portable peak flow meter or to have spirometry done before and after work. Qualitative and quantitative tests for possible air and gas triggers may also be performed.

Exercise spirometry with cycle ergometry, treadmill, or free running may be done to evaluate possible EIA. If symptoms and physical signs respond positively to the administration of bronchodilators, partially reversing the airflow measurements, this will confirm a diagnosis of asthma. Pulse oximetry will quickly measure the oxygen level in the blood.

A complete blood count (CBC) with differential white blood count (WBC) count may show an increased eosinophil count (greater than 4%) in allergic asthma. A microscopic examination of sputum may be done to determine sputum eosinophil count to monitor therapy or if an infection is suspected. Most allergic asthmatics have an elevated specialized protein (total serum immunoglobulin E, or IgE) level in their blood. Skin testing for allergens may be done in some individuals, or blood radioallergosorbent tests (RAST) may be performed to determine factors involved in precipitating attacks.

Treatment

Medications for control of chronic asthma fall into 2 categories: quick relief (reliever) medications or long-term control (controller) medications.

Acute asthma exacerbations are treated with short-acting beta-agonists such as salbutamol that work by relaxing the smooth muscles surrounding the bronchi and bronchioles, anticholinergics such as ipratropium bromide (for severe exacerbations), and systemic oral or intravenous (IV) corticosteroids. Oxygen may also be needed to alleviate hypoxia in asthma refractory to usual medications. If the attack is severe and prolonged, the individual will be admitted to the hospital for intensive treatment because respiratory failure and death can occur. In-patient treatment might require a positive-pressure oxygen mask or mechanical ventilation (respirator).

Treatment of chronic asthma includes inhaled bronchodilators (sympathomimetics and parasympatholytics), anti-inflammatory medications (inhaled steroids, inhaled cromolyns, and leukotriene modifiers), theophyllines (currently used less commonly), and decreased exposure to causative agents. The goal with these medications is to stabilize lung function and decrease the likelihood of developing acute asthma symptoms.

Bronchodilators are generally used as asthma "rescue medications" to relieve coughing, wheezing, shortness of breath, and difficulty in breathing. They can be short-acting drugs or long-term controller drugs and may also be used before exposure to a known asthma trigger to decrease any potential bronchospasm. They are the primary medication for EIA, usually provided in a metered-dose inhaler (MDI).

Anti-inflammatory agents such as corticosteroids reduce asthma symptoms. Inhaled corticosteroids are the cornerstone of asthma treatment because they act to reduce inflammation, which is thought to decrease disease progression.

Many of the cells that cause airway inflammation are known to produce potent chemicals within the body called leukotrienes. Leukotrienes are responsible for contracting the smooth muscles of the airway, increasing fluid leakage from blood vessels in the lung, and promoting inflammation by attracting other inflammatory cells into the airways. Oral anti-leukotriene medications help fight the inflammatory response and are used to treat chronic asthma.

A recombinant DNA-derived humanized immunoglobulin G monoclonal antibody is a newer drug that binds to the excess IgE on mast cell and basophil surfaces, reducing the release of mediators that cause the allergic response.

Newer immunomodulating drugs are also available and show promise in the management of moderate to severe persistent asthma; however, no long-term benefit is observed yet, and there is a relatively high risk of side effects.

Antihistamines may be prescribed to relieve or prevent the symptoms of allergic rhinitis (hay fever) and other allergies. Decongestants are used to treat nasal congestion and other symptoms by shrinking blood vessels, thereby decreasing the amount of fluid that leaks out and reducing nasal congestion.

Aggressive treatment of any respiratory or pulmonary infections associated with an asthma exacerbation is recommended, along with immunization against influenza and pneumococcal pneumonia.

Prognosis

The outcome in asthma is variable. Nearly 3 out of every 5 individuals with asthma have some limitation in their daily lives due to the disease (CDC). A mild asthmatic attack may be treated easily with an extra dose of inhaled bronchodilator. A severe asthmatic attack might lead to severe, prolonged asthma, hospitalization, and multiple complications. If the individual's airways remain chronically inflamed, permanent disability may occur. The keys to a good outcome are daily peak flow monitoring, strict compliance with medications, and avoidance of known triggers.

Complications

Free air or gas within the pleural cavity (pneumothorax) or the abnormal presence of air in central compartment of the thoracic cavity (pneumomediastinum) can develop during severe asthma attacks, especially if the individual requires mechanical ventilation. A severe asthma attack that does not respond to usual treatment can lead to prolonged contraction (bronchospasm) of smooth muscles (acute severe asthma, formerly known as status asthmaticus) that requires very aggressive treatment and may lead to respiratory failure and death. Individuals who have chronic pulmonary disease in addition to asthma will often have more severe and debilitating episodes of asthma.

Long-term oral steroid use by asthmatics can lead to blood chemistry disturbances, cataracts, osteoporosis, immunosuppression, and adrenal suppression (exogenous Cushing syndrome). Over-treatment of asthma with bronchodilators may precipitate cardiac arrhythmia.

Ability to Work (Return to Work Considerations)

Avoiding fumes, gases, dust, extreme temperatures, and any other airway irritants known to trigger an attack is essential. Masks and/or respirators should be used when required. When asthma is triggered by exercise or exertion, the individual should first be given the opportunity to use preventive medication and, if that is ineffective, be reassigned to less strenuous duties.

For more information on risk, capacity, and tolerance, refer to "Work Ability and Return to Work," pages 302-306.

Maximum Medical Improvement

Failure to Recover

If an individual fails to recover within the expected maximum duration period, the reader may wish to consider the following questions to better understand the specifics of an individual's medical case.

Regarding diagnosis:

Does individual complain of wheezing, coughing, chest tightness, and shortness of breath?

References

Cited

"Asthma Fact Sheet." Centers for Disease Control and Prevention. U.S. Department of Health and Human Services. 17 Apr. 2014 <http://www.cdc.gov/asthma/impacts_nation/asthmafactsheet.pdf>.

"Methodology and Acknowledgements: Calculations of Populations-at-Risk." State of the Air. 2013. American Lung Association. 18 Apr. 2014 <http://www.stateoftheair.org/2013/key-findings/methodology-and-acknowledgements.html#calculations>.

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